- Atonia, atony, atonic
- Atopy NEC V15.09
- Atransferrinemia, congenital 273.8
- Atresia, atretic (congenital) 759.89
- Atrichia, atrichosis 704.00
- Atrioventricularis commune 745.69
- Atrophia - see also Atrophy
- Atrophoderma, atrophodermia 701.9
- Atrophy, atrophic
- Attack
- Attention to
- Attrition
- Atypical - see also condition
- Atypism, cervix 622.10
- Audible tinnitus (see also Tinnitus) 388.30
- Auditory - see condition
- Audry's syndrome (acropachyderma) 757.39
- Aujeszky's disease 078.89
- Aura
- Aurantiasis, cutis 278.3
- Auricle, auricular - see condition
- Auriculotemporal syndrome 350.8